Tungsten contact-breaker arm



NW. 29, m7. 1,650,897 A. J. LIEBMANN TUNGS'I'EN CONTACT BREAKER FiledOct. 50. 1924 Inventor: bAlfred J. Liebmcmn 1:] His Attornegq.

spinning the shank Fatented Nov. 2%, llFZF;

ALFRED I. LIEBIl/IANN,

OF NEW YORK. N. 55, ASSIGNOR T0 GENERAL ELEGTRICU 00M lAIiiY, ACORPORATION OF NEMV YORK.

"PUNGSTEN CONTACT-BEEAKER ARM.

application filed @ctobcr 30, 195.24%. fierial No. 74.6,?23.

My invention relates to devices formaking and breaking electric circuitsand more particularly to breaker or distributor arms provided withcontacts of tungsten or similar high melting metal and constructed tovibrate to make and break a circuit in which the contacting elements arerequired to engage with a high degree of precision in order to reducesparking to a minimum. Such breaker arms are commonly used in mag netos,ignition systems for automobiles, and similar devices.

Contact points or elements of tungsten are well adapted for use inmaking and breaking electric circuits, such as the ignition circuits ofautomobiles. The circuit is usually controlled by two cooperatingcontacts of tungsten, one of which is stationary and secured to the endof a steel screw to be adjustable, and the other is secured to avibrating breaker arm which is moved to bring the contact points intoand out of engagement. Heretofore the contact point in the breaker armconsisted of atungsten disc attachedto the head of a steel rivet whichin turn was riveted in place on the breaker arm. Accurate positioning ofthe riveted contact point is diiiicult because there must be in the arma hole larger than the shank of the rivet to permit the contact point tobe riveted to the arm, and the position of the contact point isuncertain to the extent of the clearance between the shank of the rivetand the edge of the hole. In many cases, the shanks of the contactpoints are not riveted or spun over to the proper extent, so that thecontacts are loose on the arm, do not operate properly, and make a poorelectrical contact'with the arm. Another serious disadvantage is thefrequency with which the tungsten face of the contact point is marred,cracked, or otherwise injured during the operations of riveting or ofthe contact point.

VVorn' out contacts are often replaced by riveting new, but inferior,contact points to the original arm causing faulty operation, and injuryto the reputation of the e uipment in which the breaker arm is usefacture.

lln accordance with my invention the contact of tungsten or other highmelting metal is very accurately positioned on the contact arm bywelding the contact to a projection formed on the contact arm during itsmanu- A convenient way of accomplishing this result is to stamp or pressin a flat part of a sheet steel contact arm a cup or depression, therebyraising on the other side of the contact arm a very accuratelypositioned projection or table, and to weld to the top of this table atungsten contact disc of substantially the diameter and shape of thetable and accurately centered on the t ble, the contact armand tungstendisc becoming practically integral and together constituting a veryaccurately made breaker arm. A convenient way is to weld the disc to thesteel arm by means of a linking layer of a metal, such as copper or ofan alloy, which wets or alloys with both tungsten and steel. By thisproperty of wetting, the copper when fused forms a fluid meniscusbetween the tungsten and steel whereby forces due to the surface tensionthereof operate to obtain equilibrium and centre substantiallyaccurately the tungsten disc over the projection on the contact arm.

My invention will best be understood in connection with the accompanyingdrawing, inwhich it have illustrated some forms of breaker arms, and inwhich Figure 1 is a side elevation of a sample form of arm constructedin accordance with my invention; Figure 2 is a plan view of the armshown in Figure 1; Figure 3 is a cross-section along the line 3-3 ofFigure 1; and Figure 4: is a longitudinal section of another form ofarm.

The particular form of contact arm shown in Figure 1 is stamped orpressed out of one piece of sheet metal, such as sheet steel; and hasperforated ears 1 on flanges 2 which form part of and stiffen the flatWeb 3 of the arm. At the point where the contact point is to be securedto the arm a cup or depression 3, thereby producing on the other side aprojection or table 5, preferably circular, and

with its top somewhat above the level of the surface of the web 3.

To mount the contact disc accurately upon the table 5, I prefer to use alinking layer 6 of some metal, such as copper, or brass, or similaralloy, which melts at a temperature below that at which the metal of thearm softens, and which, when melted, will adhere to or wet the metal ofthe arm and also the metal of the contact disc. In the particularembodiment of the invention shown a circular disc oftungstenof'substantially the same diameter as the circular table 5 isused, and I find that upon the melting of the copper linking layer 6 thetungsten contact 7 automatically centers itself upon the table, so thatwhen the linking layer cools the tungsten point is not ,only welded tothe table, but is very accurately centered on it.

In the practice of my invention the tungsten disc 7 is placed upon acopper disc which is about the diameter of the tungsten contact disc andrests upon the table 5, as illustrated in Figure 3. The assemblage isthen heated in a muffle furnace in an atmosphere of hydrogen, until thecopper disc 6 melts, wetting both the sheet steel contact arm and thetungsten contact point, whereupon, because of the forces above referredto operating in the melted copper, the tungsten contact point 7 centersitself very accurately upon the table, and remains centered as theassemblage cools down, with the result that the accurately positionedcontact point is r firmly welded to the contact arm.

A marked commercial advantage of my invention is that the contact armwhich the tungsten disc welded to it forms a unitary integral breakerarm upon which the maker can place his name and trade-mark, as indicatedin Fig. 2. Breaker arms of this type on which the contact discs are wornout are replaced by genuine ones made by the original manufacturer,because the worn out tungsten contact cannot be replaced by riveting tothe old contact arm a new but inferior contact. The contact disc is moreaccurately and permanently positioned than is feasible with rivetedcontact points, and the electrical conductivity is very much better thanwhere the contact point is secured to the arm by riveting.

Figure 4 is a longitudinal section of another form of breaker arm inwhich the contact disc is welded to the table on the arm and isrmanently in proper relation to the remain er of the arm.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A contact arm adapted for precision make and break service inelectrical circuits, comprising a body member of sheet steel deformed tohave a. pivotal supporting portion and a substantially flat supportingsurface struck up at a desired distance from said pivotal supportingportion, a contact element of tungsten having substantially the samesize and shape as said supporting surface, and an interposed layer ofbrazing material having a relatively low melting point and adapted towet when melted both tungsten and steel whereby, when fused, it operatesboth to centre and to weld said contact element to said body member.

2. A contact arm adapted for precision make and break service inelectrical circuits, comprising a body member of up-set sheet steelformed with a portion having a relatively flat surface, a dependingportion providing an axis of oscillation parallel to said flat surface,and a struck-up circular table portion spaced a desired distance fromsaid axis, a circular contact element of tungsten having substantiallythe same cross-sectional area as said table portion, and a linking layerof copper interposed between said element and said table portion andadapted when brought to a welding temperature to center said contactelement upon the said table whereby said element is in a predeterminedrelation to said axis and projects above said surface portion, havingits cylindrical axis normal to the surface of said surface portion.

3. A method of manufacturing vibrating contact arms of sheet metal whichare adepted for precision make-and-break service in electrical circuits,comprising forming the body of the arm from sheet metal shaped toprovide pivotal support, striking up from the surface of the same asubstantially flat projecting portion, providing a refractory metalliccontact element adapted to be affixed to said projecting portion and ofthe same size and shape, and welding the latter to said struck-upportion by means of interposed material ada ted to melt at a temperaturelower than either the metal of said arm or of said contact element andto centre automatically said element upon said projecting portion by thesurface tension thereof when fused.

In witness whereof, I have hereunto set my hand this 24th do. ofOctober, 1924.

, ALFR D J. LIEBMANN.

